Composite cylinder blocks are known. For example the cylinders may be constituted by a component bolted to a separate upper crankcase. Alternatively the individual cylinders may comprise liners pressed into a block/crankcase jacket. More recently it has been proposed to cast a crankcase jacket onto a core defining the cylinders to form a unitary component. These techniques have generally been adopted to allow lightweight materials to reduce cylinder block mass, typically by providing for iron cylinders and a jacket/crankcase of aluminium alloy. Reduction in cost and ease of machining may also be important factors.
A composite cylinder block may have many advantages of performance in addition to economy of mass production. However costs of machining and assembly may be increased, along with some risk of reduced reliability consequent upon the multiple components.
Whatever method of production, a cylinder block is generally designed to have lowest possible mass and is accordingly narrow in the direction transverse to the cylinder bore. Low mass has benefits of low cost and easier materials handling. In a unitary cylinder block, the runners linking the cylinders to the outer face tend to have a large volume for reasons of good casting technique—in consequence the ribs which remain after casting have a much larger volume, and thus weight, than is required for strength and intended duty. A narrow cylinder block is preferred to reduce the volume of such ribs to a minimum, but the passages connecting the internal spaces are somewhat tortuous so that windage losses are increased.
Refinement of engine operation is essential in modern vehicles so as to reduce the transmission of noise and vibration to the occupants. This can be achieved to some extent by stiffening the cylinder block, or by using stronger materials. These solutions also tend to increase cost because a relatively stiff block may require additional mass, and strong materials tend to be expensive to form, and to machine.
What is required is a cylinder block which can provide a relatively stiff, low mass component, using low cost materials where possible, yet avoiding narrow internal spaces.
It is an aim of the present invention to address this issue and to improve upon known technology. Embodiments of the invention may provide a cylinder block for an engine which improves manufacturability without compromising performance and reliability or increasing cost. Other aims and advantages of the invention will become apparent from the following description claims and drawings.